Generally you would reduce your reported income to include only the portion that is actually income to you. For example if you collected $107 from a customer and $7 was for sales tax you would record your income as $100. This way you are only reporting income and do not need to deduct sales tax separately.
If you want to report the full amount collected as income you can deduct sales tax as an expense under "Other Common Business Expenses" and then "Taxes". You will not see a specific category for Sales Tax.
